Conventionally, a system which employs an inverter to control a motor for causing a vehicle to travel has been adopted. Generally, electric vehicles, hybrid vehicles, fuel cell vehicles and other similar electrically powered vehicles have their traveling motors outputting torque as controlled by an inverter. Typically, the motor outputs torque as controlled through PWM control. In PWM control, a carrier wave signal (a carrier signal) and a voltage command are compared in voltage and an inverter has a switching element switched on/off in accordance therewith to apply pulse width modulated voltage to the motor.
The switching operation in the PWM control results in the inverter causing noise. To address this disadvantage, for example Japanese Patent Laying-Open No. 2002-171606 (PTL 1) discloses switching an inverter's switching frequency randomly to reduce noise.